一种陡峭截止的曲面三阶带通频率选择表面天线罩设计

针对传统频率选择表面（Frequency Selective Surface,FSS）天线罩存在结构剖面高以及带外截止性能不足等问题,提出了一种K波段具有带外陡峭截止的低剖面带通型FSS天线罩设计方法。该方法通过采用多层非谐振型FSS单元结构及其电磁强耦合设计,实现了K波段三阶带通频率选择滤波特性。该天线罩不仅具有极低的剖面,而且实现了通带到阻带的快速陡峭过渡。进一步采用多层电路板压合技术和天线罩敷制工艺加工了该K波段曲面FSS天线罩样件,不仅保证了天线罩的图案加工精度,同时也确保了复杂曲面成型精度。最后,进行了天线罩传输特性及对天线方向图影响的测试验证,测试结果与设计结果吻合较好,证明了设计方法的可行性。     

利用时域有限差分法分析共面波导的频率选择特性

共面波导(CPW)中的微带单元采用不同形式时，进行级联后，会产生频率选择性作用，能得到有带通滤波特性的结构。运用时域有限差分法(FDTD)对一种具体结构进行分析，可以得到宽频域内散射曲线的实际情况，适当地选择参数就可以设计出能运用于实际印刷电路设计中的高性能频率选择性器件。     

一种双频段有源频率选择表面的设计

在频率选择表面问题的研究中,当传统FSS结构成型后,其工作带宽和谐振频率等参数固定,不能适应外部电磁环境的变化.为解决上述问题,设计了一种有源FSS结构,在传统FSS中加载PIN管或变容二极管等有源器件,通过调节器件的偏置电压或电流来改变FSS的电磁特性;运用等效电路法分析了有源FSS结构的传输线模型,利用有限元软件HFSS研究了不同加载方式下,该结构的电磁响应变化;通过有源FSS结构单元与传统FSS结构单元的交替排列,实现了具有双频性质的FSS结构.研究结果表明FSS加载电容时,谐振频率降低,且加载电容值越大,谐振频率越低,带宽越小;FSS加载电感时,谐振频率增大,且加载电感值越小,谐振频率越高,带宽越大.结果表明,为在实际应用中达到带宽优化的效果,应尽可能加载较小的电容与电感.     

高精度曲面建模优化方案

目的 为了进一步提高高精度曲面建模（HASM）方法的模拟精度和计算速度,进而拓宽该模型的应用领域,提出了新的HASM模型算法。方法 采用新的差分格式计算HASM高斯方程中的一阶偏导数,以HASM预处理共轭梯度算法为例分析改进的差分格式对HASM的优化效果。结果 数值实验表明：在计算耗时及内存需求不变的情况下,采用新的差分格式的HASM算法可以显著提高单次迭代的模拟精度,同时能够降低关键采样点缺失对模拟结果精度的影响。进一步研究发现,当HASM采用新差分格式与原始差分格式（中心差分）交替迭代时,能够快速降低模拟结果的误差。结论 本文算法当达到指定的精度条时能够显著减小计算耗时,同时还能降低关键采样点缺失对模拟结果的影响。     

基于有源频率选择表面的波束扫描天线设计

为减少使用的有源元件数量,本文提出了一种新型的基于有源频率选择表面的波束扫描天线。该天线由简单的单极子天线和10列频率选择表面组成,其中单极子天线作为辐射源放置在频率选择表面所构成的圆柱中心位置。通过控制所加载PIN二极管的工作状态,可将重新配置天线波束。整个天线尺寸为0.35λ_o×0.35λ_o×0.98λ_o(λ_o是自由波长)。实测结果表明,所设计的波束扫描天线的工作频率为2.45GHz,主波束可以实现在整个水平面的扫描,扫描精度为36°,并且天线在整个工作频段内的增益都大于6dBi,峰值增益是7.95dBi。该波束扫描天线可用于智能通信系统中。     

高精度曲面建模优化方案研究

目的：为了进一步提高高精度曲面建模（HASM）方法的模拟精度和计算速度,进而拓宽该模型的应用领域。方法：本研究采用新的差分格式计算HASM高斯方程中的一阶偏导数,以HASM预处理共轭梯度算法为例分析了改进的差分格式对HASM的优化效果。结果：数值试验表明：在计算耗时及内存需求不变的情况下,采用新的差分格式的HASM算法可以显著提高单次迭代的模拟精度,同时能够降低关键采样点缺失对模拟结果精度的影响。进一步研究发现,当HASM采用新差分格式与原始差分格式（中心差分）交替迭代时,能够快速降低模拟结果的误差。结论：本文基于HASM模型控制方程的离散差分改进格式,提出了新的HASM模型算法,新算法一方面当达到指定的精度条时能够显著减小计算耗时,另一方面还能降低关键采样点缺失对模拟结果的影响。     

一种窄带三维频率选择表面

提出了一种双极化窄带三维频率选择表面。该频率选择表面由若干个相同的单元结构周期排列构成,每个单元结构包括一个方形金属筒和一个方形介质块。方形介质块的上下表面刻有一对相同的耶路撒冷金属十字,中间层为带有四个相同矩形孔径的方形金属板。单元结构的上下表面谐振结构通过中间层矩形孔径发生电磁耦合作用,产生了两个传输极点,形成了平坦二阶通带响应。此外,在通带右侧产生了两个传输零点,频率选择和带外抑制性能得到了提升。同时该频率选择表面在双极化模式下具有良好的角度稳定性。     

基于子域基函数的任意频率选择表面数值分析

频率选择表面的电磁散射特性问题是飞行器隐身技术中的重要研究内容.采用了谱域法和子域屋顶基函数相结合的方法对任意单元形状的周期结构进行分析.首先将单元划分成若干个小网格,每个网格上的电流密度用屋顶基函数表征,然后通过电流密度和散射场的关系以及边界条件,得到导体面上的感应电流,从而分析结构的反射和传输特性.同时给出了贴片型、环形和孔径型的仿真算例,分析了单元上的电流分布规律,并与仿真的结果进行比较分析,验证了方法的有效性和通用性.     

Ku波段宽带传输频率选择表面优化设计

通过调整频率选择表面(FSS)单元的结构参数来控制电磁波在某雷达波段内的传输是滤波器研究领域的重要内容。为实现圆环形FSS单元在Ku波段的宽带传输特性,并明确单元结构参数对其传输特性的影响规律,采用谱域分析法,从圆环形单元的大小、宽度、阵列周期等方面,对圆环形单元FSS进行了数值分析和优化设计。仿真结果表明,谐振频率点的主要影响因素为单元大小,而单元宽度主要控制传输带宽。经优化,当单元外半径为3.5mm,单元宽度为0.66mm,阵列周期为10.0mm时,谐振频率为14.8GHz,FSS传输带位于Ku波段内,传输带宽达5.7GHz。优化后的FSS结构适用于Ku波段宽带传输,为优化设计提供了依据。     

A Progressive Radiosity Algorithm for Scenes Containing Curved Surfaces

Based on the theory of light energy transfer between two differential diffuse surface areas, a generalized radiosity approach is presented. Unlike the conventional radiosity method, curved surfaces are subdivided into triangular surface patches, radiosity is assummed to be vary across each triangular surface patch. By adopting linear interpolation scheme over each triangular surface patch, we have established a complete set of approximated radiosity equations. Their unknowns are radiosities of differential surface areas located at all vertices of surface patches. The generalized radiosity equation has also been extended to non-diffuse environments. Theoretical analysis and experimental results demonstrate the great potential of this method,     

用ToolBook演示空间曲线曲面

本文提出了用ToolBook制作软件演示空间曲线和曲面形成的动态过程的几种方法,并给出了详细的程序。     

High-Order Mixed Current Basis Functions for Electromagnetic Scattering of Curved Surfaces

We construct high-order mixed current vector basis (unctions on an arbitrary curved surface which can be subdivided as a union of curved triangles and quadrilaterals. The objective is to construct vector basis (a) which consists of high-order polynomials of the surface parameterization variables on triangles and quadrilaterals, (b) part of the basis will have vanishing moments on the triangles and quadrilaterals. The first property will enable us to represent the current distribution over scatter surface with much less number of unknowns and larger patches of either triangular or quadrilateral shapes. The second property will achieve what wavelet basis does on an interval, but on a more general domain, namely, a sparse matrix representation for some integral operators.     

Computing Local Surface Orientation and Shape from Texture for Curved Surfaces

Shape from texture is best analyzed in two stages, analogous to stereopsis and structure from motion: (a) Computing the texture distortion from the image, and (b) Interpreting the texture distortion to infer the orientation and shape of the surface in the scene. We model the texture distortion for a given point and direction on the image plane as an affine transformation and derive the relationship between the parameters of this transformation and the shape parameters. We have developed a technique for estimating affine transforms between nearby image patches which is based on solving a system of linear constraints derived from a differential analysis. One need not explicitly identify texels or make restrictive assumptions about the nature of the texture such as isotropy. We use non-linear minimization of a least squares error criterion to recover the surface orientation (slant and tilt) and shape (principal curvatures and directions) based on the estimated affine transforms in a number of different directions. A simple linear algorithm based on singular value decomposition of the linear parts of the affine transforms provides the initial guess for the minimization procedure. Experimental results on both planar and curved surfaces under perspective projection demonstrate good estimates for both orientation and shape. A sensitivity analysis yields predictions for both computer vision algorithms and human perception of shape from texture.     

Geodesic-Controlled Developable Surfaces for Modeling Paper Bending

We present a novel and effective method for modeling a developable surface to simulate paper bending in interactive and animation applications. The method exploits the representation of a developable surface as the envelope of rectifying planes of a curve in 3D, which is therefore necessarily a geodesic on the surface. We manipulate the geodesic to provide intuitive shape control for modeling paper bending. Our method ensures a natural continuous isometric deformation from a piece of bent paper to its flat state without any stretching. Test examples show that the new scheme is fast, accurate, and easy to use, thus providing an effective approach to interactive paper bending. We also show how to handle non-convex piecewise smooth developable surfaces.     

Extruder path generation for Curved Layer Fused Deposition Modeling

Extruder path generation for a new rapid prototyping technique named “Curved Layer Fused Deposition Modeling” (CLFDM) has been presented. The prototyping technique employs deposition of material in curved layers in contrast to flat layers as in Fused Deposition Modeling (FDM). The proposed method would be particularly advantageous over FDM in the manufacturing of thin, curved parts (shells) by reduction of stair-step effect, increase in strength and reduction in the number of layers. The criteria for the generation of tool paths for CLFDM are proper orientation of filaments and appropriate bonding between adjacent filaments in same layer and in successive layers.     

曲面上旅行商问题的多项式时间近似方案

欧氏旅行商问题(TSP)的多项式时间近似方案(PTAS)结合了递归剖分、动态规划两种方法.相似的技术已成功用于构造多个欧氏组合优化问题的PTAS.为进一步拓展该方法的适用范围,研究曲面上的TSP.观察到球面不像平面那样可以递归正则剖分,对于可被开半球完全覆盖的小尺度球面TSP,采用的策略为将其逆球心射影到一个球内接正方形上,扰动其顶点并构造剖分网格,接着将该网格射影到球面,然后如同平面TSP的PTAS一样进行动态规划等操作.该策略被拓展到非小尺度球面TSP及更一般的一类曲面TSP.需注意的是由于球面、平面之间射影变形的不规则性,无法将球面TSP直接PTAS归约为平面TSP.